1. Technical Field
The present invention relates to an inverter control device for driving a motor and an air conditioner.
2. Related Art
As an inverter control device for driving a general induction motor used in a general-purpose inverter, for example, an inverter control device for driving an induction motor of V/F controlled system as shown in FIG. 16 is known (see non-patent document 1).
In FIG. 16, the main circuit is composed of a DC (direct-current) power supply apparatus 113, an inverter 3, and an induction motor 4. The DC power supply apparatus 113 includes an AC (alternating-current) power source 1, a rectifying circuit 2, a smoothing capacitor 112 for accumulating electric energy for the DC voltage source of the inverter 3, and a power factor correcting reactor 111 for the AC power source 1.
On the other hand, a control circuit is composed of a V/F control pattern section 13 for determining the motor voltage value to be applied to the induction motor 4 on the basis of a speed command ω* of the induction motor 4 given from outside, a motor voltage command generator 14 for generating a voltage command of each phase of the induction motor 4 on the basis of the motor voltage value determined in the V/F control pattern section 13, and a PWM controller 18 for generating PWM signals of the inverter 3 on the basis of each phase voltage command generated from the motor voltage command generator 14. An example of general V/F control pattern section 13 is shown in FIG. 17.
As shown in FIG. 17, the motor voltage value to be applied to the induction motor 4 is uniquely determined corresponding to the speed command ω*. Generally, the speed command ω* and motor voltage value are stored as a table value in the memory of the processing unit such as a microcomputer, and the speed command ω* other than the table value is linearly interpolated from the table values, and then a motor voltage value is calculated.
Supposing the AC power source 1 to be 220 V (AC power source frequency 50 Hz), the input of the inverter 3 to be 1.5 kW, and the smoothing capacitor 112 to be 1500 μF, the relation of the harmonic components of the AC power source current and the degree about the AC power source frequency at 5 mH and 20 mH of the power factor correcting reactor 111 is shown in FIG. 18. FIG. 18 also shows the standard of IEC (International Electrotechnical Commission), in which the cubic harmonic component largely exceeds the IEC standard when the power factor correcting reactor 111 is 5 mH, but higher harmonic components of up to the degree of 40 satisfy the IEC standard at 20 mH.
Therefore, to conform to the IEC standard at high load, in particular, the inductance value of the power factor correcting-reactor 111 must be further increased, and the inverter device is increased in size and weight, and the cost is also increased.
Accordingly, as an attempt to suppress increase of inductance value of the power factor correcting reactor 111, and reduce the power source harmonic components and heighten the power factor, a DC power supply unit as shown in FIG. 19 is proposed (for example, see patent document 1).
In FIG. 19, an AC supply voltage of the AC power source 1 is applied to an AC input terminal of a full-wave rectifying circuit composed of bridge connection of diodes D1 to D4, and its output is charged into an intermediate capacitor C by way of a reactor Lin, and the electric charge of this intermediate capacitor C is discharged into a smoothing capacitor CD, and a DC voltage is applied to a load resistance RL. In this case, a transistor Q1 is connected to positive and negative DC current paths connecting the load side of the reactor Lin and the intermediate capacitor C, and this transistor Q1 is driven by a base driving circuit G1.
Pulse generating circuits I1 and I2 for applying a pulse voltage to the base driving circuit G1, and a dummy resistance Rdm are further provided. The pulse generating circuits I1, I2 are composed of a circuit for detecting the zero cross point of AC supply voltage, and a pulse current circuit for causing a pulse current to flow through the dummy resistance Rdm until the momentary value of the AC supply voltage becomes equal to the voltage across the intermediate capacitor C from the time zero cross point is detected.
Herein, the pulse generating circuit I1 generates a pulse voltage in the front half of a half cycle of the AC supply voltage, and the pulse generating circuit I2 generates a pulse voltage in the latter half of a half cycle of the AC supply voltage.
When flowing a current by force to the reactor Lin by turning on the transistor Q1, a reverse flow preventive diode D5 is connected so that the electric charge in the intermediate capacitor C may not be discharged through the transistor Q1, and further in the path of discharging the electric charge of the intermediate capacitor C into the smoothing capacitor, a reverse flow preventive diode D6 and a reactor Ldc for enhancing the smoothing effect are connected in series.
In this configuration, by turning on the transistor Q1 in part or all of a phase interval in which the momentary value of the AC supply voltage does not exceed the voltage across the intermediate capacitor C, reduction of harmonic components and improvement of power factor can be achieved while preventing the device size from increasing.                Patent document 1: Japanese Laid-open Patent Publication No. 9-266674.        Non-patent document 1: “Inverter Drive Handbook”, pages 661–711 (ed. by Inverter Drive Handbook Editors Committee, first edition, 1995, Nikkan Kogyo Shimbunsha).        
In the conventional configuration, however, large capacity of the smoothing capacitor CD and reactor Lin are still required (patent document 1 discloses results of simulation at 1500 μF, 6.2 mH), it also includes the intermediate capacitor C, transistor Q1, base driving circuit G1, pulse generating circuits I1, I2, dummy resistance Rdm, reverse flow preventive diodes D5, D6, and smoothing effect enhancing reactor Ldc, and therefore the device is large in size and great in the number of parts, and hence the cost is increased.